Designers of cargo containers have long faced many related challenges in the design of container sidewalls. First, the structural integrity of the overall container depends on the rigidity and strength of the sidewalls. Second, the sidewalls are optimally light in weight to reduce the transportation costs for the overall container.
Third, government regulations and industry standards often limit the exterior dimensions of cargo containers. Thus, to maximize the capacity of the container, designers of cargo containers seek to minimize the width of the walls of the container without compromising the structural integrity of the container.
Fourth, because cargo containers are repeatedly loaded and unloaded, the interior walls of the container must be resistant to the repeated impact of vehicles and implements used to load and unload the container, and must also optimally be free of protrusions and snag points that could impede the loading or unloading of the container. Fifth, means for securing and dividing cargo within a container are often desirable, and may be provided by incorporating logistics slots in the sidewalls of the container. Other considerations, including the cost and availability of the sidewall components and the ease of manufacturing the sidewalls, are also important.
These challenges are particularly acute in the design and construction of sidewalls for over-the-road trailers. Structural integrity for trailers is of course essential to the safe transportation of goods and materials on public highways. This structural integrity may be provided by vertical posts or ribs incorporated in the sidewalls of the trailer. In this prior art design, known as “sheet and post” construction, the vertical posts are typically formed by bending or roll forming galvanized steel or extruding aluminum into a wide variety of cross sections. Relatively thin sidewall panels, typically made of plywood or plastic, are attached to the vertical posts in the interior of the trailer and a protective outer skin, typically made of very thin aluminum, is attached to the vertical posts on the exterior of the trailer. A protective metal, wood or plastic liner may be provided at the base of the interior sidewall to protect the panels and posts from being damaged or pierced by vehicles loading and unloading the trailer.
The vertical posts used in “sheet and post” trailer sidewall designs have been made with a wide variety of cross sections. Although widely varied in specific design, these posts share the common feature and advantage of increased rigidity based on the cross-section of the posts, which resists bending both perpendicular and parallel to the plane of the trailer sidewall. This rigidity provides the essential structural integrity for the trailer.
An alternative to “sheet and post” construction is structural panel trailer sidewall construction. In this design, the trailer sidewall panels or plates, rather than posts, provide the essential structural integrity for the trailer. These structural panels may be made of solid aluminum, but are more conventionally a composite panel constructed of a core plastic material and an outer skin of aluminum or steel. These composite panels are typically joined at their edges with vertical splicer plates on the inside and the outside of the trailer, as shown in U.S. Pat. No. 4,904,017 (FIG. 9) issued to Ehrlich.
The use of composite panels provides many advantages in the construction of trailers. In particular, because of the strength and rigidity of the composite panels, trailer sidewall thickness can generally be reduced as compared to conventional sheet and post designs. Current state and federal regulations limit the exterior width of a trailer to 102.38 inches. Using composite panels joined with plates, the thickness of the trailer sidewalls can be reduced to less than 0.625 inches each, providing an interior width of at least 101 inches. This additional interior width greatly increases the interior capacity of the trailer and the options for loading and storing cargo in the trailer.
Composite panel designs, however, must overcome the problem of creating snag points or protrusions on the interior of the trailer where the panels are joined. Snag points or protrusions on the inside of the trailer may cause cargo, pallets and loading vehicles to catch on the interior wall of the trailer as cargo is loaded and unloaded, thus creating the potential for damage to cargo and the trailer sidewall. Therefore, it is desirable for the sidewalls of the trailer to be free of snag points and protrusions.
To address this issue, some composite panels have been coined at their ends so as to compress the plastic core and create a recessed portion along the edge of the panel, as shown in U.S. Pat. No. 5,860,693 (FIG. 2) issued to Ehrlich. The coined panels with recessed edges are then joined with a splicer plate. Because the splicer plate seats in the recessed edges, the interior wall of the trailer is relatively free of snag points and protrusions.
As noted in U.S. Pat. No. 6,450,564 issued to Sill, however, coining the edges of a composite panel creates certain problems. Sill notes that the coining of the edges “either reduces the amount of core material at the edges, or severely compresses it,” thereby compromising the structure of the composite sidewalls. Sill addresses this problem, as shown in the '564 patent (FIG. 3) and also U.S. Pat. No. 6,578,902 (FIGS. 4 and 5), by bending and offsetting the edges of the composite panel so as to form a plateau recessed from the main plateau of the composite panel. The composite panels with bent, offset edges are then joined with a splicer plate. Again, because the splicer plate seats in the recessed plateau along the edges of the composite panels, the interior wall of the trailer is relatively free of snag points and protrusions.
Alternatives and improvements to these prior art configurations for joining composite plates are desirable. In particular, the use of a post rather than a flat splicer plate provides certain advantages. Because the non-linear cross-section of a post increases the bending resistance both perpendicular and parallel to the plane of the trailer sidewall, this increased rigidity improves the structural integrity of the trailer. The use of a post with a non-linear cross-section, however, presents certain challenges that must be overcome to avoid substantially increasing the total thickness of the trailer sidewall and also to avoid creating snag points and protrusions on the interior of the trailer.
Accordingly, an object of the present invention is to provide a sidewall construction for a cargo container that utilizes posts rather than flat splicer plates to join composite plates to provide increased structural integrity for the container.
A further object of the present invention is to provide a cargo container with sidewalls of minimum overall thickness to maximize the capacity of the container.
Yet another object of the present invention is to provide a cargo container with interior walls free of protrusions and snag points that could impede the loading or unloading of the container.
An additional object of the present invention is to provide a cargo container using composite panels that are lightweight yet thin, rigid, strong, highly durable and easily replaced in the event of damage to a panel.
A still further object of the present invention is to provide a cargo container with interior logistics slots in the sidewalls of the container for securing cargo loaded into the container.
Finally, an object of the present invention is to provide a cargo container sidewall configuration that that is economical to manufacture and refined in appearance.